The interior ministry said at least one of the policemen who died had been shot.

The violence continued through the day and into the night. The army - which has stayed on the sidelines during other recent violence - moved in to separate the two sides but did not get actively involved, AP said.

The agency said protesters climbed on tanks, shouting: "The people and the army are one hand!", urging the military to take their side.

There has been widespread antagonism towards the police since the mass protests which brought down former President Hosni Mubarak in February 2011.

Many people believe the police stood by, allowing the football riots which led to the deaths of 74 people, mainly supporters of Cairo's al-Ahly team, in revenge for their support for the anti-Mubarak protests.

A court is due to deliver verdicts against the 39 defendants on 9 March.